Although the present inventions are not limited thereto, a blade server is one example of data processing apparatus in which metal-based (e.g. copper-based) data transfer can be problematic. Blade servers are comprehensive computing systems that include processors and other application specific integrated circuits (ASICs), memory, storage, and associated electronics all on a circuit board. One or more server blades may be contained in an enclosure, along with server appliance blades, network-switch blades, storage blades, management blades, local-area-network (LAN) blades, and other blades. An ASIC may include one or more data processors which perform data processing operations in parallel with one or more ASICs on the same circuit board and which may communicate with the ASICs of other circuit boards in the system. The rearward end of the blades frequently includes connectors that mate with backplane connectors on the chassis within the enclosure when the blades are inserted into the enclosure. With respect to cooling, many blade server enclosures include fans or other blowers which create airflow. The air typically flows from the forward end of the blades to rearward end and over the electronic components.
The data communication between the blades is often through metal-based backplane data connections. One issue associated with metal-based backplane data connections stems from the fact that increases in data transfer may necessitate larger backplane data connectors, which can interfere with the air flow that is required for cooling. There are also issues associated with the use of metal-based data connections between components, e.g. between a central processing unit (CPU), memory and storage. Specifically, in order to form an efficiently functioning unit, the components must be located as close as possible to one another. This typically results in each blade including all of the components necessary for it to act as an efficiently functioning unit.
One proposed solution to some of the issues described above is to employ optical communication between circuit boards. For example, each board may include an array of light emitters and detectors that can communicate with one another. The present inventors have determined that such optical communication between boards may be challenging. For example, mechanical misalignment during installation, the operation of hard disk drive, and the air turbulence associated with cooling can result in circuit board vibrations that adversely effect free space optical links or require the use of costly mechanical coupling components. Also, free space optical communication can be adversely effected by the dust associated with air cooling and can require strenuous optics or dynamic steering of the beam to compensate for the board to board spacing and vibration. Optical backplane connections have also been proposed. However, in order to accommodate optical backplane connections, the associated enclosure must have an optical pathway routed through backplane, which can be expensive because it requires costly coupling components, and is inefficient in terms of the link budget and power consumption.